1. Field of the Invention
This invention relates generally to electrode structures useful in electrochemical cells and, more particularly, this invention relates to a method of forming consumable reactive metal anodes having a perimeter seal.
2. Description of the Prior Art
Electrochemical cells utilizing consumable, reactive metal anodes are well known. Typically, the anode comprises an alkali metal, such as lithium, in elemental, compound or complex form, in conjunction with a cathode and an aqueous or non-aqueous electrolyte. In a preferred form, the anode is lithium, and the electrolyte comprises an aqueous solution of lithium hydroxide.
Such cells are described in detail in numerous patents and publications, including U.S. Pat. Nos. 3,791,871 (Rowley); 3,976,509 (Tsai et al); 4,007,057 (Littauer et al); and 4,188,462 (Klootwyk), the respective disclosures of which are incorporated herein by reference.
The anode typically is in the form of a disc, plate, or other structure having at least one surface which contacts the electrolyte during operation, and another surface or edge which perimetrically surrounds at least a portion of the electrolyte-contacting surface of the anode. Due to the well-known reaction of the anodic metal with the electrolyte, which results in the consumption of the anode, a seal around the perimetric surface is necessary for useful operation of the anode. If such sealing is not adequate, the anode wears unevenly about the perimeter, resulting in significantly decreased battery power and energy output, while proportionately increasing the cell's heat and hydrogen gas output rate.
Prior attempts to provide effective seals for reactive metal anodes have met with only limited success. Prior anode edge seals have been standard solid gasket materials or, alternatively, a coating of heavy rubber paint. Solid gaskets are inadequate in that they involve considerable weight, volume and complexity. Such gaskets invariably leak and, therefore, are only partially effective.
Heavy rubber paint coatings are inadequate in that the anode face which contacts the electrolyte is consumed and thus recedes during normal cell operation, leaving intact the rubber edge coating, which greatly disturbs electrolyte flow patterns, especially in multi-cell structures. Also, the rubber flap which remains after partial consumption of the anode face obstructs the anode, lowering power and energy output while increasing hydrogen gas and heat production rates.